Power Electronics-1 - May 2013

Electronics Engineering (Semester 6)

TOTAL MARKS: 80
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Assume data if required.
(4) Figures to the right indicate full marks. 1 (a) What are the minimum requirements to turn on the SCR?(4 marks) 1 (b) Explain two transistor analogy of SCR. (4 marks) 1 (c) What are the characteristics of ideal power semiconductor devices?(4 marks) 1 (d) Explain four modes of working of TRIAC.(4 marks) 1 (e) Compare power BJT, MOSFET and IGBT.(4 marks) 2 (a) What is the meaning of commutation of SCR? Explain any two methods in detail.(10 marks) 2 (b) Explain the role of UJT as a relaxation oscillator. Draw the appropriate waveforms.(10 marks) 3 (a) Explain the single phase full wave fully controlled rectifier for inductive load.(10 marks) 3 (b) Explain the series connection of SCR. What are the problems associated with this connection?(10 marks) 4 (a) Explain the three phase controlled rectifier for resistive load. Draw the output waveform for firing angle of 30° and 60°.(10 marks) 4 (b) What are the protection circuits for SCR? Explain each circuit in brief.(10 marks) 5 (a) Explain the DIAC-TRIAC circuit for regulating the intensity of light. (Light Dimmer circuit).(10 marks) 5 (b) If the half-wave controlled rectifier has a purely load of R and the delay angle is &alpha=?/3. Determine:
(i) Rectification Eficiency
(ii)Form Factor
(iii) Ripple Factor. (10 marks) 6 (a) Derive the performance factors namely; Input displacement factor, Input power factor, DC Voltage, Voltage ratio, Input current distortion factor, Input harmonic factor and Voltage ripple factor for fully- controlled single phase rectifier (Bridge Rectifier) with R-L load. (10 marks) 6 (b) Explain the construction, working principle, V-I characteristics and applications of DIAC.(10 marks)

Write short notes on any three:-

7 (a) Power MOSFET.(7 marks) 7 (b) GTO SCR.(7 marks) 7 (c) IGBT.(7 marks) 7 (d) Cooling methods of SCR(7 marks)